1. Field of the Invention
The present invention relates to a composite bead and a fabrication method thereof, and particularly, to a porous composite bead comprising superparamagnetic cluster and nanoparticles, such as light-emitting nanoparticles, magnetic nanoparticles, metallic nanoparticles, metal oxide nanoparticles and the like, and a fabrication method thereof.
2. Background of the Invention
A composite bead containing a light-emitting material or metal has excellent physicochemical characteristics so as to be expected to have high usability for a material for LEDs or displays, photonic crystal lasers, biosensors, environment-related sensors and the like, accordingly, many researches for various types of composite beads are widely undergoing.
Meanwhile, in order to use composite beads in fields requiring fast analysis within several minutes, such as portable sensors or environment-related sensors, it may be better to take a shorter time for recovering composite beads and have superior dispersion properties. Especially, a recovering process should be performed within a short time using superparamagnetic properties or the like, and the superior dispersion properties are required when it is not a recovering process.
A research for allowing magnetic nanoparticles to be situated near a bead surface has been conducted, however, the number of superparamagnetic nanoparticles was not able to exceed more than 5% of the number of fluorescent nanoparticles due to the characteristic of the fabrication process, which caused difficulty to recover composite beads using a magnetic field. For the composite beads according to the related art, the superparamagnetic nanoparticles occupied 0.05% or less of the entire weight of the composite bead in a size of submicron to micron. Hence, it took a long time of about 5 to 10 hours to recover composite is beads by setting a typical laboratory magnet thereto.
Even in structures that a mixture of superparamagnetic nanoparticles and fluorescent nanoparticles was present within the bead (Journal of the American Chemical Society, 2006, 128, 688-689), like a raisin bun, or near a surface of the bead (ACS nano, 2008, 2, 197-202), since the weight of superparamagnetic nanoparticles merely occupied 0.5% or less of the composite bead, it also took a long time to be attracted under a magnetic field. Furthermore, due to the structure like the plum cake, the fluorescence emitted from the fluorescent nanoparticles situated deep in the composite beads was drastically decreased rather than that emitted from the fluorescent nanoparticles present independently.
In the meantime, the use of ferromagnetic or ferrimagnetic particles has an advantage of a quick response under a magnetic field; however, even for non-existence of a magnetic field, a strong cohesion is exhibited among magnetic particles, accordingly, the composite bead particles including those particles problematically have an extremely low dispersion properties.
Hence, a structure is required in which the dispersion property in case of the non-existence of the magnetic field is improved by increasing the content of superparamagnetic particles within the composite bead and faster attraction is expected upon applying a magnetic field. Also, in addition to solving the problem, there are needed composite beads having superior functionalities, such as optical properties of nanoparticles in a composite bead structure.
That is, composite beads, which are attracted by a typical laboratory magnet within at least several minutes and simultaneously has an excellent functionality such as optical property and exhibits a superior dispersion property in case of non-existence of a magnetic field, are more preferable to be used for sensors or the like. However, any composite bead satisfying such conditions has not been introduced yet.